Tomato Blight
All About Tomato Blight
There are three different kinds of tomato blight that can cause damage and even death to tomato plants. These are Septoria Leaf Spot, Early Blight and Late Blight. All of these diseases are caused by fungi and are the worst in very rainy seasons. The spores need water to spread to other plants.
Septoria Leaf Spot is caused by a fungus named Septoria lycopersici. Tomato plants may acquire the disease at any time during the growing season, whether young or old. It is distinguished by little circular spots that first begin to appear on the undersides of older leaves. Spots are gray or tan with a darker ring around the outside. They may get to be a quarter of an inch and have pimple-like growths called pycinidia. Spots hardly ever appear on the fruit but can appear on leaves, stems and blossoms. As the disease worsens the leaves will turn yellow, dry out and drop to the ground. With no leaves, the tomatoes may experience sun scalding.
Septoria Leaf Spot occurs in wet and humid conditions. The spores of the fungus can be spread from one plant to another by splashing, windblown rain, insects, human beings and cultivating equipment. The best temperature for the disease to spread is in the high seventies. If you leave diseased plants in the soil or do not till plants deep enough underground, the disease can spread from one season to the next. Potatoes and eggplants can also be affected by the disease. Be careful of nearby weeds as the fungus can live over the winter on horsenettle, smooth groundcherry, and black nightshade.
The best way to prevent Septoria Leaf Spot is to buy disease-free seeds and plants, till your tomato plants under every year right after harvesting, rotate plants, eliminate weeds, and apply fungicides designed for use on tomatoes.
Early tomato blight, Alternaria solani, is one of the most prevalent diseases in the Northeastern United States. Ideal conditions for this fungus are 80 degrees and wetness that can be caused by dew, fog, rain, mist or irrigation. The whole plant and fruit can be affected. Circular lesions as large as one-half inch can be spotted on the plant, and eventually all the leaves will die. The spores are spread by water, humans, insects, wind and machines. Do not work on or around wet tomato plants. Early tomato blight can live through the winter so fungicides should be applied and the soil tilled under immediately after harvest.
Late tomato blight is another fungus that loves wet weather and this one occurs later in the season during cooler weather. Greenish black blotches appear on the plant leaves and the undersides show a white fuzzy growth. The fruit of the plant can also have these blemishes. Late blight can easily spread to potato plants, and it was the cause of the Irish Potato Famine. Treatment is the same as for Septoria Leaf Spot and early blight.